Percutaneous interventional angioplasty procedures typically involve guide catheters introduced into the cardiovascular system and advanced through the aorta into a desired coronary artery. Using fluoroscopy, a guide wire is then advanced through the guide catheter and across an artery site to be treated, such as a blockage, lesion, stenosis, or thrombus in an artery lumen. A delivery catheter may then be advanced over the guide wire to deliver a suitable endoluminal medical device, such as a stent, graft, stent-graft, vena cava filter, or other vascular implant. In many cases, a stent is delivered to the treatment site to reinforce body vessels, keep the vessel open and unoccluded, and prevent restenosis. The stent is expanded to a predetermined size, thereby dilating the vessel so as to, for example, radially compress an atherosclerotic plaque in a lesion against the inside of the artery wall. The stent may be a mechanically expandable stent that is expanded using a balloon catheter, for example, or it may be a radially self-expanding stent utilizing resilient or shape memory materials, such as spring steel or nitinol. With respect to a balloon expandable stent, the stent is compressed or crimped about a balloon on the distal end of the catheter. The stent may be covered by an overlying sheath or sleeve to prevent the stent from becoming dislodged from the balloon. With respect to a self-expanding stent, the stent is positioned at a distal catheter end around a core lumen where it is held down (compressed) and covered by an overlying delivery sheath or sleeve. In either case, upon retraction of the sleeve, the stent is able to self-expand and/or be expanded with a balloon. In particular, it is often necessary to remove the stent delivery device and then introduce a separate balloon catheter to “seat” the deployed stent with a balloon.
During the loading and deployment of self-expanding stents, there may be significant frictional forces between the stent surface and the surrounding delivery sheath. These forces may damage the coatings on coated stents, especially longer coated stents, and can create difficulties for sheath retraction and placement. The frictional forces can cause the stent to act like a spring, releasing the stored frictional forces beyond the sheath end and causing the stent to move or “jump” from the desired position and be imprecisely deployed. In addition to the imprecise placement of self-expanding stents, it is often difficult to predict the final stent length in advance of its expansion in the vessel. Further, once a portion of the stent has expanded against the vessel walls, it becomes difficult to adjust its position. Similar problems may occur during the loading and deployment of balloon expandable stents. For example, frictional forces between the protective sheath and the stent may damage any coating on the stent.
U.S. Pat. No. 6,702,843 B1 to Brown et al. discloses a 3-tube stent delivery system, including an outer sheath; an inner sheath; a rollable balloon material folded upon itself and connecting the distal ends of an outer sheath and an inner sheath; and a stent attached around a coaxially positioned inner catheter, constrained by either the inner sheath or the rollable balloon material. An inflation lumen between the outer sheath and the inner sheath may used to dilate a vessel prior to stent deployment. When constrained by the inner sheath, the rollable balloon material may be inflated to dilate a vessel prior to delivery of the stent. When constrained by the rollable balloon material, the balloon may be inflated to seat a stent following its delivery. Brown's 3-tube system limits the size range of stents that may be employed, and depending on its construction, may limit its ability for seating a stent after deployment (when constrained by the inner sheath), or be more prone to inadvertent expansion of the stent (when constrained by the balloon material).
U.S. Pat. No. 7,201,770 B2 to Johnson et al. discloses a stent delivery system, including an outer tube, an inner tube, and a balloon affixed therebetween. An inflation lumen is defined by the space between the inner tube and the outer tube for inflating and deflating the balloon. The balloon is designed to surround and prevent (or constrain) the expansion of a compressed self-expanding stent. The balloon, extending from the distal end of the outer tube is folded back onto itself and affixed to the inner tube, proximal to the stent. When the outer tube is retracted in the proximal direction, the balloon progressively peels back to release the stent. Following release of the stent, the balloon may be positioned within the stent and inflated to fully expand or “tack” the stent in place, as necessary. Johnson characterizes “the unique arrangement of the present invention” in terms of the distal area of the balloon having a novel shape, whereby the distal section of the both the inner and outer balloon portions are tapered inward to protect the leading distal end of the stent and to provide for easier advancement of the catheter system along the desired passage for treatment (col. 2, lines 22-28). However, inasmuch as Johnson relies on the balloon to constrain the stent in a compressed state, Johnson's system risks inadvertent expansion of the stent at an undesired vessel location. Moreover, Johnson's reliance on balloon material to constrain the stent may limit the range and size of stents that can be compressively maintained without significant risk of inadvertent release.
U.S. Pat. Appl. No. 2006/0030923 to Gunderson discloses a stent delivery system comprised an outer tube, an inner tube, and a rollable membrane affixed therebetween. A fluid lumen, defined by the space between the inner tube, the rollable membrane, and the outer tube, is utilized to encourage the rolling action of the membrane and to maintain a gap between the membrane and the outer tube during retraction so as to reduce frictional forces underlying the stent's tendency to push outward against the outer tube. In another embodiment, a secondary fluid lumen extending into the stent receiving region underlying the membrane is utilized to provide a flush path for transporting fluid to the stent receiving region during or prior to delivery of the stent. Gunderson does not suggest an expandable balloon material for use in the membrane, nor does Gunderson suggest inflation of the membrane overlying the fluid lumen to dilate a vessel and/or seat a stent following initial deployment.
In view of the shortcomings and limitations in the prior art, there is a need for a reliable endoluminal medical device delivery system, which addresses the above difficulties by reducing frictional forces hampering stent delivery, by increasing the range of employable self-expanding stents for use, by reducing the risk of inadvertent stent release, and by simplifying the process for setting (or seating) a stent following deployment.